The embodiments described herein relate generally to electric machines, and more specifically, to a mechanism for securing a machine shaft to a bearing.
Rotating mechanical mechanisms typically have bearings for supporting the rotating components of the mechanism relative to the stationary components. For rolling element bearings, those having balls, rollers or spherical rollers, typically one element or race is fixed to the rotating component and the other element or race is fixed to the stationary component. The rolling elements provide for motion between one race and the other race.
Fixing the races to the rotating component and to the stationary component can be accomplished by interference fit of bores to diameter or by forces applied to the faces of the races. Due to tolerance stacks from manufacturing inaccuracies, thermal expansion of differing materials and assembly inaccuracies, providing interference fits on both races typically results in an unacceptable axial preload on the bearing.
For applications where the radial load on the bearing remains in a fixed direction during the mechanism's duty cycle the rotating component may have an interference fit to the race and the stationary component may have a clearance fit to the race. This arrangement avoids axial preload on the races. Forces in such a mechanism do not cause the race to move rotationally relative to the stationary component.
For applications where the radial load on the bearing changes direction during the mechanism's duty cycle, precession or a tendency of the race to move rotationally slightly during the duty cycle often occurs. This precession may cause fretting or wear on the shaft or housing. The fretting and wear can create particles that may migrate through the mechanism. The particles may propagate into the lubricant and into the bearing rolling elements, leading to shortened bearing life.
Alternatively, a feature on the race bore, the race outside diameter or race face may cooperate with a feature on the rotating component and to the stationary component, typically a shaft or housing, to provide physical interference between the race and the component. Such features, however, add significant costs and provide stress risers to the race and component.
The present invention is directed to alleviate at least some of these problems with the prior art.